(;AW[ba]AB[bb]AB[cb]AB[db]AB[eb]AB[bd]AB[cd]AW[bf]AW[af]AW[ce]AW[be]AW[dd]AW[fb]AW[fa]AW[ea]AW[ec]AW[ed]AW[fe]AW[df]AP[goproblems]
(;W[da];B[ca]
(;W[ad];B[ac];W[cc];B[bc]TR[aa]TR[dc])
(;W[cc];B[bc]TR[dc]TR[aa])
(;W[bc];B[ac])
(;W[ac];B[ad];W[ab];B[bc])
(;W[aa];B[ab];W[ad];B[dc])
(;W[ab];B[ac]))
(;W[ab];B[ac])
(;W[aa];B[ac])
(;W[bc];B[ac])
(;W[ac];B[ad])
(;W[dc];B[cc];W[da];B[ca]
(;W[ac];B[ad];W[ab];B[aa]C[Ko fight for bent-four, Black takes first. You can do better.])
(;W[ab];B[ac])
(;W[ad];B[ac])
(;W[aa];B[ac]))
(;W[ad];B[ac];W[cc];B[bc];W[dc];B[aa];W[ab]TR[ca]C[Ko, White takes first. Black cannot play C19 because of shortage of liberties. But you can do better!])
(;W[cc];B[dc]
(;W[da];B[ca]
(;W[ad];B[bc];W[ab];B[aa]C[Close!])
(;W[ab];B[bc];W[ad];B[aa]C[Close!])
(;W[ac];B[bc]))
(;W[ac];B[bc])
(;W[ad];B[bc]
(;W[da];B[ca];W[ab];B[aa]C[Close!])
(;W[ab];B[ac]
(;W[da]C[Very nice!RIGHT])
(;W[ca]C[RIGHT])))
(;W[ab];B[bc]
(;W[ad];B[ac]
(;W[da]C[Very nice!RIGHT])
(;W[ca]C[RIGHT]))
(;W[da];B[ca];W[ad]))))